Objective: To report the first real-world case of an Alzheimer's disease patient who achieved PET-defined amyloid clearance sufficient to meet the discontinuation criteria and successfully discontinue donanemab therapy, and to illustrate the feasibility of PET-guided individualized treatment duration in clinical practice.

Methods: A 78-year-old female patient with AD was systematically evaluated before and after donanemab therapy. Cognitive function, amyloid-β (Aβ) and Tau PET imaging, and MRI findings were longitudinally monitored, along with the assessment of treatment-related adverse events.

Results: After six infusions of donanemab, the patient's Aβ load decreased to 7.02 Centiloids (CL), meeting the predefined discontinuation criterion. Tau deposition showed a mild visual reduction compared with baseline. The MoCA score increased from 17 to 21, mainly in the orientation domain, while activities of daily living remained stable. Asymptomatic amyloid-related imaging abnormalities (ARIA) was detected and remained stable during follow-up

Conclusion: This case demonstrates that donanemab can achieve substantial Aβ clearance with favorable safety in real-world settings. PET-based quantitative guidance for individualized therapy duration appears feasible, though long-term follow-up is required to assess the durability of Aβ clearance and its downstream impact on Tau dynamics and clinical outcomes, providing insights for precision application of anti-Aβ therapies.